1. Field of the Invention
The present invention relates to a circuit element, a resonator, a filter, a duplexer, and a high-frequency circuit device, for example, used in the microwave band or millimeter wave band, for use in wireless communication devices or electromagnetic wave transmission/reception devices.
2. Description of the Related Art
Typically, planar resonators used in the microwave band or millimeter wave band are formed of a planar circuit, such as a microstrip line, placed on a dielectric substrate.
Compact planar resonators having the above configuration are disclosed in the following references:
(1) Ikuo AWAI, xe2x80x9cPlanar Microwave Filtersxe2x80x9d, MWE 2000 Microwave Workshop Digest, pp. 445-454, 2000; and
(2) Morikazu SAGAWA and Mitsuo MAKIMOTO, xe2x80x9cGeometrical Structure and Fundamental Characteristics of Microwave Stepped-Impedance Resonatorsxe2x80x9d, Technical Report of IEICE, SAT95-76, MW95-118 (1995-12), pp. 25-30, 1995.
The resonators disclosed in the above references comprise a so-called stepped-impedance resonator having a line whose width is stepped so as to provide a low impedance at an open side thereof and a high impedance at a shorted side thereof. That is, when the impedance at the open side of a resonator line is high and the impedance at the shorted side is low, and the impedance ratio is greater, the wavelength shortening effect increases, thus allowing the overall resonator to be compact.
The wavelength shortening effect is now described with reference to FIGS. 18A to 18E.
FIG. 18A depicts the line pattern of a resonator having a stepless structure, and FIG. 18B depicts the line pattern of a stepped-impedance resonator. FIG. 18C depicts a resonator according to an embodiment of the present invention, as described below. FIG. 18D is an equivalent circuit diagram of the resonators depicted in FIGS. 18A and 18B. FIG. 18E is a graph showing the relationship between the ratio of impedance Z1 at the open side and impedance Z2 at the shorted side and the normalized line length (wavelength shortening coefficient).
In FIG. 18D, Z1 denotes the impedance at the open side, Z2 denotes the impedance at the shorted side, xcex81 denotes the electrical length at the open side, and xcex82 denotes the electrical length at the shorted side.
For example, if xcex81:xcex82=5:5, i.e., with a stepped-impedance resonator in which the length at the open side is equal to the length at the shorted side, where Z1/Z2=0.5, then the normalized line length kr will be 0.784. Thus, the stepped-impedance resonator shown in FIG. 18B has a resonator line whose line length is reduced by a factor of about 0.78 with respect to the resonator, shown in FIG. 18A, which is not a stepped-impedance resonator.
The wavelength shortening effect is highest when xcex81:xcex82=5:5, i.e., an equal step.
In order to achieve a high wavelength shortening effect using such a stepped-impedance resonator, the impedance ratio must be high. However, the line width of the low-impedance portion cannot be so large since the area on a dielectric substrate is restricted, resulting in a relatively small line width at the high-impedance portion. Thus, the resonator operates with the small-line-width portion exhibiting a peak in the current distribution, thereby causing high conductor loss and low Q in the resonator.
The problem of low Q must be overcome not only in resonators, but also in other high-frequency circuit elements such as capacitors. It is also important to improve the compatibility when connecting such elements to a low-loss line to form a circuit.
Accordingly, it is an object of the present invention to provide a compact and low-loss conductive line element, and a resonator, a filter, a duplexer, and a high-frequency circuit device incorporating the conductive line element.
To this end, in one aspect, the present invention provides a multi-spiral element including a group of spiral conductive lines. The spiral conductive lines are arranged so as not to cross each other so that the spiral conductive lines are substantially rotationally symmetric with respect to a predetermined point on a substrate. A plurality of conductive lines in the group of spiral conductive lines have external peripheral ends aligned at a substantially straight line substantially orthogonal to the conductive lines.
In this configuration, one spiral conductive line is adjacent to another spiral conductive line having substantially the same configuration as that spiral conductive line, and a gap is formed between the conductive lines, through which a magnetic field orthogonal to the dielectric substrate extends. This prevents the magnetic field from being concentrated at the edges of an electrode so as to make the magnetic field uniform, thus mitigating the edge effect in each of the spiral conductive lines. Therefore, the current concentration at the edges of each spiral conductive line can be reduced. As a result, the overall conductor loss is reduced, thus reducing the loss in the multi-spiral element.
Since the external peripheral ends of the conductive lines in the multi-spiral element are aligned at a straight line substantially orthogonal to the conductive lines, the multi-spiral element can be readily connected to, for example, a straight-line-group element having a plurality of substantially straight conductive lines which are substantially parallel to each other so that the straight conductive lines do not cross the spiral conductive lines. Thus, loss at the connection therebetween can be minimized.
In another aspect, the present invention provides a resonator including the above multi-spiral element. The multi-spiral element is connected to each end of a straight-line-group element having a plurality of substantially straight conductive lines substantially parallel to each other.
The multi-spiral element serves as a compact and low-loss capacitor for accumulating a charge, while the straight-line-group element serves as a compact and low-loss inductor. Therefore, a compact and low-loss resonator can be achieved.
In still another aspect, the present invention provides a resonator including two of the above resonators. Each of the resonators is linearly symmetric, in which the spiral conductive lines in the multi-spiral elements connected to both ends of the straight-line-group element are reversely turned with respect to each other. The straight-line-group element in one of the resonators is adjacent to the straight-line-group element in the other resonator, and four of the multi-spiral elements are horizontally and vertically substantially symmetric with each other.
Therefore, the conductor loss can be reduced in the straight-line-group element, thus increasing the Q factor in the overall resonator.
In still another aspect, the present invention provides a filter in which a signal input and output unit is provided for the above-described resonator. A compact and low-insertion-loss filter can be therefore achieved.
In still another aspect, the present invention provides a duplexer including two of the above-described filters. The signal input and output unit comprises a transmission-signal input terminal, input and output terminals for transmission and reception, and a received-signal output terminal. A compact and low-insertion-loss duplexer can be therefore achieved.
In still another aspect, the present invention provides a high-frequency circuit device including the above-described multi-spiral element, the above-described resonator, the above-described filter, or the above-described duplexer. A compact and low-insertion-loss high-frequency circuit can be therefore achieved. A communication apparatus incorporating such a high-frequency circuit can increase communication quality including a noise characteristic and a transmission rate.